1. Field of the Invention
This invention relates to a pressure sensor adaptable, for example, to sensing pressure in the combustion chamber or chambers of an internal combustion engine.
2. Description of the Prior Art
It is well-known to indirectly sense pressure in the combustion chamber of an internal combustion engine by means of an external device attached to the engine cylinder head. This pressure sensor takes the form of a washer and fits around a cylinder head bolt attaching the cylinder head to the engine cylinder block. The pressure sensor is clamped between the cylinder head and the bolt in a manner similar to a normal washer. The pressure sensor includes a piezoelectric element deformed by the force resulting from air/fuel mixture combustion in the engine cylinder. The piezoelectric element serves to generate an electrical signal reflecting the pressure in the combustion chamber.
Generally, the accuracy of piezoelectric elements in sensing force or pressure decreases as their internal stress increases. In the above-mentioned pressure sensor, the piezoelectric element is continuously under intense stress due to the static clamping force between the cylinder head and the cylinder block. As a result, the accuracy of this pressure sensor is relatively low.